<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>圆角 椭圆 太极</title>
    <style>
        .halfCycle{
            width: 200px;
            height: 100px;
            margin: 100px auto;
            border: 10px solid #000;
            box-sizing: border-box;
            /*border-radius: 50%;*/
            border-top-left-radius: 100px;
            border-top-right-radius: 100px;
        }

        .ellipse{
            width: 200px;
            height: 100px;
            margin: 100px auto;
            border: 10px solid #000;
            box-sizing: border-box;
            border-top-left-radius: 100px 50px;
            border-top-right-radius:  100px 50px;
            border-bottom-left-radius:  100px 50px;
            border-bottom-right-radius:  100px 50px;
        }

        .tj{
            width: 200px;
            height: 200px;
            margin: 100px auto;
            box-sizing: content-box;
            border: 1px solid #000;
            margin: 100px auto;
        }

        .tj .top{
            width: 200px;
            height: 100px;
            box-sizing: border-box;
            border: 1px solid #0f0;
            border-radius: 100px 100px 0 0;
            position: relative;
            background-color: #0f0;
        }

        .tj .bottom{
            width: 200px;
            height: 100px;
            box-sizing: border-box;
            border: 1px solid #f00;
            border-radius: 0 0 100px 100px;
            position: relative;
            background-color: #f00;
        }

        .tj .center{
            width: 100px;
            height: 100px;
            box-sizing: border-box;
            border: 1px solid #f00;
            border-radius: 50%;

        }

        .tj .top .center{
            border: 30px solid #0f0;
            position: absolute;
            left: 0;
            top: 50%;
            background-color: #fff;
            z-index: 1;
        }

        .tj .bottom .center{
            border: 30px solid #f00;
            position: absolute;
            right: 0;
            top: -50%;
            background-color: #fff;
        }


    </style>
</head>
<body>
<!--半圆-->
<div class="halfCycle">
    半圆
</div>

<div class="ellipse">
    椭圆
</div>

<div class="tj">
    <div class="top">
        <div class="center"></div>
    </div>
    <div class="bottom">
        <div class="center"></div>
    </div>
</div>
</body>
</html>